**3. Types of insecticides and their modes of action**

There are many classes of insecticides with varying modes of action. The insecticides used in different vector control programmes are generally classified into four classes on the basis of their chemistry, toxicological action, or their mode of penetration, *viz.,* organochlorines, organophosphates, carbamates, synthetic pyrethroids insect growth regulators and bacterial larvicides (**Figure 1**).
